1. Field of the Invention
This invention relates to a method of safely constructing a power supply system in obtaining high voltage by series connection of a plurality of batteries.
2. Description of the Related Art
Automobile and railcar industries have been developing a system for driving an induction motor by a power converter using a storage battery as its power supply, which allows for construction of environment-friendly systems with high mileage, low emission, and low noise.
On the other hand, toward a high-capacity battery for use in the above system, a battery module having an output voltage of about 170 volts has been developed. A unit of two such battery modules connected in series is used in automobile applications. In railcar applications, in some cases, four such battery modules are connected in series.
Batteries, in contrast to capacitors, cannot be completely discharged. In particular, overdischarge accelerates degradation of storage batteries such as nickel metal hydride and lithium ion batteries. For this reason, special care must be taken to avoid electric shock in handling conventional battery modules as described above, which have a total voltage of as high as about 700 volts when four modules are connected in series.